listview优化和异步加载全攻略

package cn.wangmeng.test; import java.util.List; import cn.wangmeng.test.AsyncImageLoader.ImageCallback; import android.app.Activity; import android.graphics.drawable.Drawable; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.ArrayAdapter; import android.widget.ImageView; import android.widget.ListView; import android.widget.TextView; /** * 数据适配器类 *@author hsx *@date 2012-11-21 *@Description */ public class ImageAndTextListAdapter extends ArrayAdapter<ImageAndText> { private ListView listView; private AsyncImageLoader asyncImageLoader; /** * 构造函数 * @param activity * @param imageAndTexts * @param listView */ public ImageAndTextListAdapter(Activity activity, List<ImageAndText> mData, ListView listView) { super(activity, 0, mData); this.listView = listView; asyncImageLoader = new AsyncImageLoader(); } public View getView(int position, View convertView, ViewGroup parent) { Activity activity = (Activity) getContext(); ViewHolder holder = null; // if (convertView == null) // { /** * 装载listview的布局文件 */ LayoutInflater inflater = activity.getLayoutInflater(); convertView = inflater.inflate(R.layout.image_and_text_row, null); /** * 将convertView赋给viewholder的构造函数，赋给了ViewHolder的baseView */ holder = new ViewHolder(convertView); convertView.setTag(holder); // } /** * 此处容易发生listview显示混乱问题 */ // else // { // holder = (ViewHolder) convertView.getTag(); // } /** * 获取mData中的每一项 */ ImageAndText imageAndText = getItem(position); // 装载图片 String imageUrl = imageAndText.getImageUrl(); ImageView imageView = holder.getImageView(); imageView.setTag(imageUrl); // Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl, // new ImageCallback() // { // public void imageLoaded(Drawable imageDrawable, String imageUrl) // { // /** // * 此方法中的imageUrl实际上是前面那个imageUrl经过多次传递得到的，实际上就是图片的imageUrl // */ // ImageView imageViewByTag = (ImageView) listView.findViewWithTag(imageUrl); // if (imageViewByTag != null) // { // imageViewByTag.setImageDrawable(imageDrawable); // } // } // }); Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl,new ImageCallbackImp()); if (cachedImage == null) { imageView.setImageResource(R.drawable.default_image); }else { imageView.setImageDrawable(cachedImage); } // 装载文字信息 TextView textView = holder.getTextView(); textView.setText(imageAndText.getText()); return convertView; } public class ImageCallbackImp implements ImageCallback { public void imageLoaded(Drawable imageDrawable, String imageUrl) { /** * 此方法中的imageUrl实际上是前面那个imageUrl经过多次传递得到的，实际上就是图片的imageUrl */ ImageView imageViewByTag = (ImageView) listView.findViewWithTag(imageUrl); if (imageViewByTag != null) { imageViewByTag.setImageDrawable(imageDrawable); } } } }